Process for heat treating titaniumcopper alloy



3,078,199 PRUCESS FOR HEAT TREATING THTANIUM- CGPPER ALLOY Charles R. McKinsey, Niagara Falls, N.Y., assignor to gnign Carbide Corporation, a corporation of New or No Drawing. Filed Apr. 8, 1959, Ser. No. 804,867 1 Clai. (Cl. 148-433) This invention relates to binary titanium-base alloys and, more particularly to a titanium-copper alloy.

Among the many excellent properties which have interested the metals and chemicals industries in titanium is the high resistance to corrosion possessed by this extremely versatile metal. Titanium is already in competition with nickel-base alloys in corrosion applications, and only production and cost difliculties prevent the full utilization of titanium in many other corrosion fields, such as those dominated by stainless steels. The heretofore imposing challenge of the higher cost of titanium products plus the difiiculties involved in casting the extremely reactive molten titanium into suitable shapes have prevented the full exploitation of titaniums valuable property of high resistance to corrosion.

By alloying titanium with other metals the melting point can be reduced and the tendency of the titanium to react with crucibles and molds can also be reduced. For casting operations, it is most desirable to employ a low melting point alloy. in order to significantly reduce the melting point of the reactive metal titanium, however, it is necessary to use relatively large amounts of the alloying additive. The alloying elements which most appreciably depress the melting point of titanium form intermetallic compounds with titanium. It has, therefore, been presumed that embrittlement would result.

It is the primary object of this invention, therefore, to provide a binary titanium-base alloy having a reduced melting point lower than that of the metal titanium, which alloy possesses a useful combination of strength and ductility.

It is another object of this invention to provide a castable binary titanium-base alloy which possesses excellent corrosion resistance.

Other aims and advantages of the invention will be apparent from the following description and appended claim.

In accordance with the present invention, a binary alloy is provided consisting essentially of from about 7 to about 17 percent by weight copper and the balance substantially all titanium.

While in many binary titanium-base alloys the presence of an intermetallic compound may cause embrittlement, the addition of copper in the range specified does not result in a brittle titanium-base alloy, but rather yields a useful material having desirable mechanical and chemical properties.

The alloy produced in accordance with this invention is a hypereutectoid titanium alloy. Despite the presence of a considerable quantity of the intermetallic phase of copper and titanium, the alloy exhibits useful ductility. The alloy is amenable to strengthening and ductilityimproving heat treatments that produce a quite stable structure.

The alloy of this invention may be prepared by the same conventional arc-melting techniques which are used for the preparation of other titanium-base alloys. Be cause of the addition of copper to titanium, the resulting alloy possesses a maximum melting point about 180 C. below that of unalloyed titanium.

In the practice of this invention a binary titaniumice base alloy was produced from titanium metal having a Brinell hardness number of 72 and containing the following impurities by weight: 0.01 percent carbon, 0.025 percent oxygen, 0.001 percent nitrogen, 0.010 percent hydrogen, and less than 0.005 percent iron. To this titanium base was added copper metal of 99.9 plus percent by weight copper with less than 0.01 percent iron in an amount sufficient to constitute approximately 11 percent by weight of the resulting titanium-copper alloy. Compacts of this composition, each weighing about 30 grams, were arc-melted by a tungsten electrode in an argon atmosphere, and were finally combined to produce a gram specimen. This was remelted several times to insure complete homogeneity of the alloy ingredients in the cast specimen. The cast specimen was machined for testing and the chips were chemically analyzed. The analysis showed the alloy to be 11.1 percent by weight copper and the balance titanium and incidental impurities.

The machined specimen was then hot rolled to %-inch diameter rod at temperatures within the beta range. The alloy exhibited excellent hot working characteristics in this operation.

Tensile test blanks were prepared for heat treatment by being sealed in heat resistant glass capsules. These capsules were then evaculated and refilled with argon to a partial pressure of 0.2 atmosphere and then heated in a muffle furnace. The heat-treatment consisted of heating the specimen to 950 C. for 2 hours and water-quenching, followed by heating to 850 C. for 24 hours and water quenching, followed by heating to 750 C. for 48 hours and water quenching. This heat-treatment consists of heating the alloy at a temperature such that the alloy is within the beta field, followed by cooling below the eutectoid temperature, followed by heating above the eutectoid temperature, cooling below the eutectoid temperature and reheating below the eutectoid temperature. While this heat-treatment was effective in producing highly stable structures having the excellent properties shown in Table 1, other heat treatments may be used to prevent embrittlement of the alloy and to generally develop the properties of the alloy. A particularly eiiective heat treatment consists of heating the alloy at a temperature within the beta field, followed by cooling the alloy below the eutectoid temperature, heating the alloy at a temperature below the eutectoid temperature, and cooling the alloy.

The heat-treated tensile blanks were machined to standard As-inch diameter samples and tested at the usual strain rates for titanium. Stress-strain curves were obtained from which the 0.2 percent ofi'set yield strength and modulus of elasticity were determined. These values are shown below.

TABLE 1 Tensile Test Data Yield Ultimate Elonga- Reduction Strength, Strength, tion, Perof area, 0.2% otiset, psi. cent in percent p.s.i. in.

The specimens also exhibited a hardness correspond ing to a value of 210 in a Vickers hardness test using a IO-kg. load. The modulus of elasticity was 18.1 X 10 p.s.1.

Corrosion tests were conducted on samples of the alloy to show its excellent resistance to corrosion and its resulting suitability for use in the chemical industry. These tests were performed on specimens which were heat-treated as described above. The tests were also performed on 316 stainless steel and on a commercial nickel base alloy containing molybdenum and chromium to provide a comparative basis for the tests. In these tests, the alloy samples wereweighed, immersed in boiling 30 percent ferric chloride for from 48 to 60 hours, re moved, washed and weighed again to determine the amount of corrosion. Similar alloy samples were tested in the same manner in 30 percent nitric acid maintained at a temperature of 190 C. The corrosion rates were calculated for all the samples and are reported as mils penetration per year in Table 2.

TABLE 2 Comparative Corrosion Resistance Corrosion Rate, Mills penetration per year Sample in 30% ENG; in boiling 30% at 190 C. FeCla 11.1% Copper-Titanium Alloy 129 2.26. 316 Stainless Steel 1,690 Dissolves. A commercial Ni-Base alloy contain- Dissolves Do.

ing Mo and Cr.

ultimate strength in excess of 85,000 pounds per square inch, an elongation of about 20 percent, and a corrosion rate in 30 percent nitric acid at 190 C. of less than 200 mils penetration per year.

The description of the invention above has been in terms of its specific embodiments. Modifications and equivalents will be apparent to those skilled in the art and this disclosure is intended to be illustrative of, but not necessarily to constitute a limitation upon, the scope of the invention.

What is claimed is:

A process for producing a titanium-base alloy characterized by useful ductility comprising preparing an alloy consisting essentially of about 11 percent by weight copper and the balance titanium and incidental impurities, heating the alloy at a temperature of about 950 C. for about 2 hours, quenching the alloy in water, thereupon reheating the alloy at a temperature of about 850 C. for about 24 hours, quenching the alloy in water, and reheating the alloy at a temperature of about 750 C. for about 48 hours and quenching the alloy inwater.

References Cited in the file of this patent 2nd edition, 

